<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<ul>
    <li>.</li>
    <li>.</li>
    <li>.</li>
</ul>

<script type="text/javascript">
    //? 将li的事件绑定到ul上 实现点击li时再加一个.
    const father = document.getElementsByTagName('ul')[0]
    //? 存在事件冒泡 所以点击li时也能触发ul的事件
    father.addEventListener("click",function (e) {
        e.target.innerText += '.'
    })

</script>
</body>
</html>
